Film forming method and manufacturing method of semiconductor device

ABSTRACT

The present invention discloses a method for forming a flattened interlayer insulating film to cover the wiring layer or the like of a semiconductor IC device, and a manufacturing method of a semiconductor device. The film-forming method of the present invention comprises the steps of preparing deposition gas containing an inert gas, and a silicon and phosphorus-containing compound having III valance phosphorus in which oxygen is bonded to at least one of bonding hands of phosphorous, and forming a silicon containing insulating film  21  containing P 2 O 3  on a substrate  101  by using said deposition gas.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for forming a flattenedinterlayer insulating film to cover the wiring layer or the like of asemiconductor integrated circuit device, and a method for manufacturinga semiconductor device.

[0003] 2. Description of the Prior Art

[0004] In recent years, with regard to a semiconductor integratedcircuit device (hereinafter, referred to as a semiconductor IC device),a progress has been made to achieve a much higher density, and anincreasing number of the structures having a multilayer wiring extendedover several layers has been used. In such a case, because of thefrequent use of, especially an aluminum material for a wiring layer, astrong request has been made to develop a method for forming a flattenedinterlayer insulating film, which can be formed at a low temperatureequal to 500° C. or lower.

[0005] Conventionally available flattening methods include: one likethat shown in FIG. 1, which performs flattening by forming a film by athermal chemical vapor deposition method (hereinafter, referred to as aTH-CVD method), a plasma enhanced chemical vapor deposition method(hereinafter, referred to as a PE-CVD method) or the like, heating theformed film, and then fluidizing the film; and one like an etch backmethod shown in FIG. 2 or a chemical mechanical polishing method(hereinafter, referred to as a CMP method) shown in FIG. 3, whichperforms flattening by removing unevenness on the surface of theinsulating film by etching or polishing.

[0006] In the case of the former method, as shown in FIG. 1A, aboro-phospho silicate glass film (hereinafter, referred to as a BPSGfilm) 4 is formed by a TH-CVD method, which uses any one of thefollowing deposition gases:

[0007] (1) SiH₄+PH₃+B₂H₆+O₂ (PH₃: phosphine)

[0008] (2) TEOS+TMOP+TMB or TEB+O₂ or O₃ (TEOS: tetraethylorthosilicate(Si(OC₂H₅)₄), TMOP: trimethylphosphate (PO(OCH₃)₃)).

[0009] Alternatively, as shown in FIG. 1A, a BPSG film 4 is formed by aPE-CVD method, which uses any one of the following deposition gases:

[0010] (1) SiH₄+PH₃+B₂H₆+O₂

[0011] (2) TEOS+TMOP+TMB or TEB+O₂.

[0012] For reference, see documents: J. Electrochem. Soc., 134.3,: 657,1987, by Williams, D. S. and Dein, E. A; J. Vac. Sci. Technol., B1,1:54, 1983, by Levin, R. M. and Evans-Lutterodt, K; Extended Abstract ofElectrochem. Soc. Spring Meeting: 31, 1971, by Sato, J. and Maeda, K.

[0013] Then, as shown in FIG. 1B, the formed BPSG film 4 is heated at atemperature of about 850° C., and fluidized to be flattened. In the caseof a phospho-silicate glass film (hereinafter, referred to as a PSGfilm), a film is formed by a TH-CVD method, a PE-CVD method or the like,which uses deposition gas generated by eliminating boron containing gas(B₂H₆, TMB or TEB) from the foregoing gas, then heated at a temperatureequal to 1000° C. or lower, and fluidized to be flattened.

[0014] In the case of the latter method, as shown in FIG. 2A and FIG.3A, firstly, a non-doped silicate glass (hereinafter, referred to as anNSG film) 5 is formed by a TH-CVD method, a PE-CVD method or the like,which uses one of the following deposition gases, and then flattened:

[0015] (1) SiH₄+O₂ (TH-CVD method or PE-CVD method)

[0016] (2) TEOS+O₂ or O₃ (TH-CVD method)

[0017] (3) TEOS+O₂ (PE-CVD method)

[0018] In the etch back method, as shown in FIG. 2B, a resist film 6 isformed on the NSG film 5 by coating method, and its surface isflattened. Then, as shown in FIG. 2C, the film 6 is subjected to etchingfrom above to form a flattened NSG film 5 a. In the CMP method, as shownin FIG. 3B, the NSG film 5 is formed, and then polished to flatten thesurface of an NSG film 5 b.

[0019] In FIGS. 1 to 3, a reference numeral 1 denotes a semiconductorsubstrate; 2 a base insulating film; and 3 a and 3 b wiring layersformed on the base insulating film 2.

[0020] Incidentally, the above-described flattening methods based on theetch back method or the CMP method are effective especially when a lowtemperature is required, because these methods can be executed withoutheating unlike the case of the flattening method based on fluidizing byheating. However, as shown in FIGS. 2 and 3, if any voids are formedbetween the wiring layers 3 a and 3 b or in other recessed partsimmediately after the insulating film 5, the voids are left unchangedeven after flattening. Currently available methods for forminginsulating films having good gap-filling capabilities include ahigh-density PE-CVD method, a PE-CVD method, an atmospheric pressureTH-CVD method, an spin-on-glass (hereinafter, referred to as SOG)coating method, and the like. However, since the described flatteningmethods use no thermal fluidity, particularly when a high densificationis attained to narrow a space between the wiring layers, recessed partscannot be completely filled.

[0021] On the other hand, in the flattening method based on fluidizingby heating, since thermal fluidity is utilized, as shown in FIG. 1,complete filling can be expected. At present, especially the BPSG film 4is frequently used for such a purpose. However, heating of at least atemperature of 850° C. must be carried out for fluidization. Thus, sucha film cannot be applied to the base film 2 of the wiring layers 3 a and3 b or the interlayer insulating film 4, where a low temperature isneeded for formation. In particular, the film cannot be applied to aninsulating film to cover the aluminum wiring layer. In this case, thetemperature of fluidization can be somewhat lowered by increasing theconcentration of boron or phosphorus. Even so, the temperature is notyet sufficiently low. Rather, new problems may occur, such as areduction in the stability or humidity resistance of the insulatingfilms 2 and 4. Similar problems may occur in the case of the PSG film,because the temperature of fluidization substantially equal to that forthe BPSG film is necessary.

[0022] As an insulating film having a low fluidization temperature, aGeBPSG film formed by adding GeO₂ to the BPSG film has been developed.However, the temperature can be lowered to about 750° C. at least. Thus,it is difficult to apply this film to the base film or the interlayerinsulating film, in which a much lower temperature is required.

SUMMARY OF THE INVENTION

[0023] A fluidization temperature should preferably be set as low aspossible not only when aluminum, copper or the like is used for wiringin a semiconductor large scale integrated circuit (hereinafter, referredto as LSI) or the like, but also to prevent the re-distribution ofimpurities in an impurity introduction region generally caused by heat.

[0024] An object of the present invention is to provide a method forforming an insulating film, capable of greatly reducing a fluidizationtemperature for flattening a surface, and a manufacturing method of asemiconductor device.

[0025] The inventors focused on the following points:

[0026] (1) the BPSG film or the phospho-silicate glass film(hereinafter, referred to as PSG film) of the conventional example is amixture of SiO₂+P₂O₅+B₂O₃, or of SiO₂+P₂O₅ (PH₃ of deposition gasSiH₄+PH₃+B₂H₆+O₂ is III valance phosphorus, and bonded with externallysupplied oxygen to generate not P₂O₃ but P₂O₅. This may be attributed tothe fact that since PH₃ itself contains no oxygen, when it is bondedwith externally supplied oxygen, stable P₂O₅ is easily generated.);

[0027] (2) in the BPSG film having the P₂O₅-SiO₂, a eutectic point forthe composition of 20 to 80 % of P₂O₅ is 850° C. theoretically, and itsfluidization temperature is dependent on the melting point of P₂O₅itself; and

[0028] (3) P₂O₃ has a melting point much lower than that of P₂O₅ asdescribed on Table 1. TABLE 1 Melting point Boiling pointP₂O_(3 (III valance)) 23.8° C. 175.4° C. P₂O_(5 (V valance)) 580 to 585°C. 300° C. (sublimation)

[0029] Accordingly, the inventors considered that a fluidizationtemperature would be lowered by mainly containing P₂O₃, instead of P₂O₅,in the BPSG film or the PSG film.

[0030] Then, the inventors came up with the idea of oxidizing aphosphorus containing compound in a state of oxygen shortage to form aBPSG or PSG film having a high-concentration of P₂O₃. As methods forsuch a purpose, the followings may be possible. That is, (1) a siliconand phosphorus-containing compound, containing phosphorus atom (P atom)in the form of III valance is used as deposition gas; and (2) by using asilicon containing compound or a silicon and phosphorus-containingcompound containing oxygen, a film is formed without adding any oxygenor ozone.

[0031] Regarding a silicon and phosphorus-containing compound,containing III valance P atom, which can be applied to the method of(1), one may be selected from silicon and phosphorus-containingcompounds having the following structural formulas:

[0032] A PSG film or the like was formed by using deposition gascontaining the silicon and phosphorus-containing compound, and by aTH-CVD method or a PE-CVD method, and examination was made as tocomponents in the formed film by X-ray fluorescence analysis (XRF) orFourier transform infrared spectroscopy (FTIR). Then, the presence ofhigh-concentration P₂O₃ in the formed film was verified. Then, afluidization temperature of 700° C. or lower was obtained.

[0033] In addition, the inventors found that it is possible to adjust afluidization temperature by controlling a concentration of P₂O₃.

[0034] The inventors also found that it is possible to easily adjust aconcentration of P₂O₃ by controlling a deposition temperature and thegas flow rate of the silicon and phosphorus-containing compound (flowrate of inert gas carrier), or by controlling a concentration ofoxidizing gas when the oxidizing gas is added.

[0035] It is now assumed that nitrogen (N₂) is used as carrier gas ofthe silicon and phosphorus-containing compound. Since N₂ is a diatomicmolecule, when a film is formed by reaction of plasma enhanceddeposition gas, N₂ is prone to be dissociated, and bonded with hydrogenin the film, leaving ammonia (NH3) in the film. According to the presentinvention, inert gas, e.g., argon or helium is used as carrier gas.Because of little reactivity of argon or helium itself, the amount ofammonia in the film can be reduced substantially to zero.

[0036] Further, the use of inert gas, e.g., argon or helium, as carriergas, resulted in the great reduction in the concentration of phosphorusduring heat treatment after deposition, enhancing controllability of theconcentration of Phosphorus.

[0037] In addition, by forming a film using only the silicon andphosphorus-containing compound, containing III valance phosphorus, theamount of carbon left in the formed film can be greatly reduced. In thiscase, the adjustment of a phosphorus concentration can be made bycontrolling the ratio of flow rates between the silicon andphosphorus-containing compound and the foregoing inert gas in thedeposition gas. Accordingly, though a silicon containing compoundcontaining no phosphorus is added in the deposition gas in theconventional method in order to adjust a phosphorus concentration, thesilicon containing compound containing no phosphorus can be eliminatedfrom the deposition gas. The silicon containing compound containing nophosphorus has Si—C bonding, causing carbon to be left duringdeposition. Thus, preferably, the addition of such a compound should beprevented as much as possible. However, the compound can be added asoccasion demands.

[0038] Furthermore, the film that has been formed is subjected tonitrogen annealing and oxygen annealing, and then heated in atmospherecontaining moisture. This process is called steam annealing. Since thesteam annealing has an oxidizing force stronger than that for normaloxygen annealing, residual III valance phosphorus is oxidized, and themoisture absorption resistance of the formed film is enhanced, making itpossible to improve film quality.

[0039] The foregoing can be established similarly for the BPSG film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIGS. 1A and 1B are sectional views showing a method for formingan interlayer insulating film, which includes flattening carried out byfluidization due to heating, according to a conventional example.

[0041]FIGS. 2A to 2C are sectional views showing a method for forming aninterlayer insulating film, which includes flattening carried out byetch back, according to a conventional example.

[0042]FIGS. 3A and 3B are sectional views showing a method for formingan interlayer insulating film, which includes flattening carried out byCMP, according to a conventional example.

[0043]FIGS. 4A to 4D are sectional views showing a method for forming aPSG film, which comprises a series of steps including a film-formingstep, according to a first embodiment of the present invention.

[0044]FIG. 5 is a graph associated with the amount of ammonia in the PSGfilm formed by the film-forming method of the first embodiment of thepresent invention and showing substrate temperature dependence thereof.

[0045]FIG. 6 is a graph showing a relation between phosphorusconcentration in the PSG film formed by the film-forming method of thefirst embodiment of the present invention, and a temperature ofannealing after film formation.

[0046]FIG. 7 is a graph showing the amount of carbon in the PSG filmformed by the film-forming method of the first embodiment of the presentinvention.

[0047]FIG. 8 is a flowchart showing the film-forming method of theembodiment of the present invention.

[0048]FIGS. 9A to 9E are sectional views showing a method for forming aPSG film, which comprises a series of steps including a film-formingstep, according to a second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] Next, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

(1) First Embodiment

[0050] Description will be made of a method for forming a PSG filmthrough a series of steps including a film-forming step according to afirst embodiment of the present invention.

[0051] As shown in FIG. 8, a series of steps include, a film-formingstep, an N₂ annealing step, an O₂ annealing step, and a steam annealingstep.

[0052] With regard to deposition gas in the film-forming step, gasgenerated by mixing a silicon and phosphorus-containing compound, inertgas and oxidizing gas was used. Silicon containing compounds containingno phosphorus should not be used.

[0053] For a phosphorus containing compound, one can be selected fromsilicon and phosphorus-containing compounds having Si—O—P structures,for which the structural formulas is shown below:

[0054] (i) phosphorus acid dimethyl trimethylsilylester (referred to asSOP-11(a), hereinafter);

[0055] (ii) phosphorous acid dimethoxy trimethylsilylester (referred toas SOP-11(b), hereinafter);

[0056] (iii) P (OSi (CH₃)₃)₃: or

[0057] (iv) P (OSi (CH₃))₂OCH₃.

[0058] Other than the above, a silicon and phosphorus-containingcompound having III valance phosphorus, and oxygen being bonded to atleast one of the bonding hands of the phosphorus, can be used. In thedescribed embodiment, SOP-11(b) was used.

[0059] For inert gas to be added to the silicon andphosphorus-containing compound, inert gas of argon (Ar) or helium (He)can be used. In the embodiment, argon (Ar) was used for the inert gas.

[0060] With regard to oxidizing gas, it is not always necessary tocontain oxidizing gas in the deposition gas. However, when contained,ozone (O₃), oxygen (O₂), NO, N₂O, NO₂, CO, CO₂, H₂O, or the like can beused as oxidizing gas. In the embodiment, oxygen (O₂) is used asoxidizing gas.

[0061] As occasion demands, a silicon containing compound containing nophosphorus may be added to the deposition gas. In this case, as such asilicon containing compound, one can be selected from alkylsilane orarylsilane (general formula R_(n)SiH_(4-n) (n=1 to 4)), alkoxysilane(general formula (RO) _(n)SiH_(4-n) (n=1 to 4)), chain siloxane (generalformula R_(n)H_(3-n)SiO (R_(k)H_(2-k)SiO) _(m)SiH_(3-n)R_(n) (n=1 to 3;k=0 to 2; m∞0)), a derivative of cyclic siloxane (general formula(RO)_(n)H_(3-n)SiOSiH_(3-n)(OR)_(n)(n=1 to 3), chain siloxane (generalformula (R_(k)H_(2-k)SiO)_(m)(k=1, 2; m∞2)), and the like. In this case,R is an alkyl group, an aryl group or its derivative.

[0062] Compounds containing silicon but no phosphorus are mainly asfollows:

[0063] (i) hexamethyl disiloxane (HMDSO): (CH₃)₃SiOSi(CH₃)₃);

[0064] (ii) tetramethyl disiloxane (TMDSO): H(CH₃)₂SiOSi(CH₃ )₂H);

[0065] (iii) hexaethyl disiloxane (HEDSO): (C₂H₅)₃SiOSi(C₂H₅)₃);

[0066] (iv) tetraethyl orthosilicate (TEOS: Si(OC₂H₅)₄);

[0067] (v) triethoxy silane (TRIES: HSi(OC₂H₅)₃); and

[0068] (vi) trimethoxy silane (TMS: HSi(OCH₃)₃).

[0069] In the steam annealing step, one made by mixing oxygen andhydrogen in a predetermined ratio is reacted to generate watermolecules, and heating is carried out in atmosphere containing the watermolecules.

[0070] Conditions for a series of steps are described below. Standardprocessing conditions are shown in tables. Processing parameters havingconditions varied to obtain comparison data are described outside thetables.

(1) Deposition Condition

[0071] TABLE 2 Deposition Standard set value Substrate temperature 250°C. RF power 150 W Total gas flow rate  1.0 slm Amount of added O₂  2sccm

[0072] The substrate temperature was changed to 100, 200, and 300° C.Since SOP-11(b) is liquid at a normal temperature, it is contained incarrier gas by bubbling. The inventors prepared two kinds of compounds,i.e., one using Ar carrier as carrier gas, and one using N₂ carrier assuch. When inert gas (Ar) was used as carrier gas, the content ofSOP-11(b) in deposition gas was adjusted by controlling the flow rate ofcarrier gas.

[0073] (ii) N₂ annealing TABLE 3 Processing Standard set valueTemperature rising rate  10° C./min. N_(2 gas flow rate)  10 slm Holdingtemperature 650° C. Holding time  15 min.

[0074] For comparison, the heat treatment temperature was changed to250, 500, and 750° C. In addition, similar processing was carried outfor a film formed by containing N₂ instead of Ar in the deposition gas.

[0075] (iii) O₂ annealing TABLE 4 Processing Standard set value O₂ gasflow rate  10 slm Holding temperature 650° C. Holding time  15 min.

[0076] (iv) Steam annealing TABLE 5 Processing Standard set value O₂ gasflow rate  6 slm H₂ gas flow rate  5 slm Holding temperature 650° C.Holding time 15 min.

[0077] Any one of O₂ annealing and steam annealing among above annealingprocesses can be ommited.

[0078] First, a substrate 101 to be deposited shown in FIG. 4A is placedin the chamber of a PE-CVD apparatus. Then, substrate heating is carriedout to hold a specified substrate temperature.

[0079] Subsequently, the foregoing deposition gas is introduced into thechamber, and plasma is generated and held for a predetermined time. Inthis way, a PSG film 21 having a specified thickness containinghigh-concentration P₂O₃ is formed. In this case, depending on theconcentration of P₂O₃ or the ratio of P₂O₃/P₂O₅, the PSG film 21 may befluidized at a temperature substantially equal to the substratetemperature during film formation. Accordingly, flattening is achievedsimultaneously with the film formation.

[0080] Then, as shown in FIG. 4B, after the formation of the PSG film 21on the substrate 101, heating for flattening is carried out in N₂atmosphere. A PSG film 21 a is fluidized to be flattened.

[0081] Then, as shown in FIG. 4C, heating is carried out in atmospherecontaining oxygen. In this way, P₂O₃ in a PSG film 14 a is oxidized andconverted to P₂O₅. As a result, a P₂O₅ concentration in a PSG film 21 bis increased to thereby stabilize the PSG film 14 a.

[0082] Then, as shown in FIG. 4D, heating is carried out in atmospherecontaining moisture. Because of a high oxidizing force of the moisture,the conversion of P₂O₃ to P₂O₅ is further promoted. Accordingly, a P₂O₅concentration in the PSG film 21 b becomes much higher.

[0083] With regard to the PSG film 21 formed in the above film-formingmethod, the amount of ammonia in the film immediately after itsformation was examined.

[0084] The result of the examination is shown in FIG. 5. Specifically,FIG. 5 shows the dependence of the amount of ammonia in the formed filmafter film formation on a substrate temperature during film formation,in which an ordinate axis shows the amount of ammonia (wt. %) in theformed film, expressed in linear scale and an abscissa axis shows asubstrate temperature (°C.), expressed in linear scale.

[0085] In the examination, a sample is subjected to thermal desorptionspectroscopy (TDS) analysis, thermally desorbed ammonia gas isquantitatively measured, and then comparison is made.

[0086] As can be understood from the result of FIG. 5, there aredifferences in the tendency of dependence and contents between the caseof using Ar as carrier gas and the case of using N₂ as the same. Whencarrier gas is Ar, the substrate temperature is not affected, and littleammonia is contained in the formed film. When carrier gas is N₂, acontent of ammonia is equal to 5 wt. % or higher, and the content isincreased corresponding to the increase of the substrate temperature.

[0087] Detection was also carried out for a concentration of phosphorusin the formed film by means of X-ray fluorescence analysis (XRF). By theXRF, a total concentration of P₂O₃+P₂O₅ in the formed film can bedetected.

[0088] The result of analysis is shown in FIG. 6. Specifically, FIG. 6shows the dependence of a phosphorus concentration in the formed Film 21a on the heat treatment temperature of N₂ annealing after filmformation, in which an ordinate axis shows a P concentration (wt. %) inthe PSG film, and an abscissa axis shows a heat treatment temperature(°C.), expressed in linear scale. “As depo” denotes a concentration ofphosphorus in the PSG film 21 immediately after film formation andbefore N₂ annealing.

[0089] As can be understood from FIG. 6, there is a difference in theconcentration of P₂O₃ or in the ratio of P₂O₃/P₂O₅ in the formed PSGfilm 21 a between the case of using Ar as carrier gas and the case ofusing N₂ as the same. The concentration of P₂O₃ or the ratio ofP₂O₃/P₂O₅ can be reduced more when Ar is used as carrier gas than whenN₂ is used as the same. For both cases, it was discovered that theconcentration of phosphorus can be adjusted by a heat treatmenttemperature.

[0090] In addition, a melting temperature or a fluidization temperatureof the PSG film 21 a for each of the above case becomes lower as theconcentration of P₂O₃ or the ratio of P₂O_(3/)P₂O₅ is higher. In theexperiment, a melting temperature or a fluidization temperature equal to700° C. or lower was obtained.

[0091] Further, FIG. 7 shows the result of examining the amount ofSi—CH₃ bonding, i.e., a carbon content, in the formed film 21 b.Specifically, an ordinate axis of FIG. 7 shows an absorption intensity(arbitrary unit) by Fourier transform infrared spectroscopy (FTIR),while an abscissa axis shows the number of waves (cm−1).

[0092] According to the result shown in FIG. 7, a content of Si—C H₃bonding in the formed film 21 b varies between the case of using Ar ascarrier gas and the case of using N₂ as the same. In other words, a peakheight of an absorption intensity is lower in the case of using Ar ascarrier gas than that in the case of using N₂ as the same, and thus acontent of Si—CH₃ bonding in the formed film 21 b is smaller.

[0093] As apparent from the foregoing, according to the first embodimentof the present invention, since a phosphorus containing compound, whichcontains III valance phosphorus, is used for deposition gas, it ispossible to form a PSG film having a high P₂O₃ content immediately afterfilm formation. Accordingly, the PSG film can be fluidized at a lowtemperature.

[0094] Moreover, inert gas, e.g., argon or helium, is used as carriergas in the deposition gas. Because of little reactivity of argon orhelium itself, the amount of ammonia in the formed film can be setsubstantially to zero. Thus, the quality of the formed film can beimproved.

(2) Second Embodiment

[0095] Next, description will be made of a method for forming a PSG filmcontaining P₂O₃ by means of PE-CVD method according to a secondembodiment of the present invention.

[0096]FIG. 8 is a flowchart showing a film-forming method according tothe second embodiment of the invention. a set of FIGS. 9A to 9F is asectional view of the film-forming method of the second embodiment ofthe present invention.

[0097] As deposition gas, mixed gas of SOP-11(b)+Ar was used. To set asufficient state of oxygen shortage, no oxygen (O₂) was added differentfrom the case of the first embodiment.

[0098] As a film-forming method, a PE-CVD method by a film formingapparatus having a well-known parallel plate type electrode was used.Plasma enhanced method by the parallel plate type electrode is a methodfor applying an RF power between upper and lower electrodes placedoppositely to each other, and then converting deposition gas betweenthese electrodes into plasma. The lower electrode serves also as asubstrate holder and, as occasion demands, power for substrate biasingmay be applied to the lower electrode.

[0099] A deposition condition is described below. TABLE 6 Depositionparameter Deposition condition SOP-11(b) (bubbling by Ar)  0.1 to 2 slmAr  0.1 to 1 slm Substrate temperature  20 to 400° C. Pressure range  66to 2667 Pa RF power 100 to 700 W Frequency  13.56 MHz Substrate biaspower  0 to 300 W Frequency  13.56 MHz or 400 kHz

[0100]FIG. 9A is a sectional view of a substrate 101 to be depositedbefore film formation. The substrate 101 is constructed in a manner thata base insulating film 12, e.g., a silicon oxidized film, is formed on asilicon substrate (semiconductor substrate) 11, and wiring layers 13 aand 13 b composed of, e.g., aluminum films, are formed on the baseinsulating film 12.

[0101] In this state, first, the substrate 101 is placed on thesubstrate holder in a deposition chamber. Subsequently, the substrate101 is heated or controlled to a temperature of the range of 20 to 400°C.

[0102] Then, as shown in FIG. 9B, mixed gas of SOP-11(b)+Ar isintroduced into a plasma chamber, and gas pressure is maintained at 0.5to 20 Torr. Ar is used as carrier gas of SOP-11(b). A flow rate of Arcarrier gas containing SOP-11(b) was set in the range of 0.1 to 2 SLM,and a flow rate of added Ar was set in the range of 0.1 to 1 SLM.

[0103] Then, power 0 to 300 W of a frequency 13.56 MHz is applied to thesubstrate holder, and a bias voltage is applied to the substrate 101.Further, power 50 to 2.3 kW of a frequency 13.56 MHz is applied to theupper electrode, and deposition gas is converted into plasma.

[0104] Accordingly, reaction occurs in the plasma of the deposition gas,and the deposition of a reactive product on the substrate 101 isstarted. A PSG film 16 under film formation showed a flowability to flowinto a recessed part between the wiring layers 13 a and 13 b even at thesubstrate temperature of about 200° C. In this case, phosphorus may becontained in the PSG film 16 in the form of III valance P₂O₃. Because ofno external supply of oxygen, the state of an oxygen shortage ismaintained in a reaction system, and Si and P may be respectivelycontained in the PSG film 16 in the form of Si—O and P—O being bondedwith oxygen atoms present in molecules.

[0105] Then, after its removal from the film-forming apparatus, thesubstrate 101 is conveyed in vacuum or atmosphere, and set in a heattreatment furnace held at a deposition temperature or lower.Subsequently, as shown in FIG. 9C, N₂ is introduced into the heattreatment furnace at a flow rate of 10 SLM, and the substrate 101 isheated. A temperature rising rate is set about 10° C./min., and afterthe substrate temperature reaches 650° C, this state is maintained forseveral minutes. The processing comes to an end with the passage ofabout 15 minutes after the temperature rising. N₂ annealing breaks theglass structure of a formed film 15 a, and re-flowing brings about voidfilling and formed film flattening. In addition, a gas componentcontained in the formed film 15 a is eliminated therefrom duringheating, and thus a PSG film 15 a having III valance phosphorus isformed.

[0106] Then, as shown in FIG. 9D, while the substrate temperature ismaintained at 650° C., oxygen is introduced at a flow rate of 10 SLM,and the substrate 101 is heated in oxygen atmosphere for about 15minutes. III valance phosphorus has very high reactivity, and is proneto be oxidized. Thus, the phosphorus can be converted into stable Vvalance phosphorus by exposing it to oxygen atmosphere at a hightemperature. In this way, the PSG film 15 a containing the unstable IIIvalance phosphorus becomes a PSG film 15 b containing stable V valancephosphorus.

[0107] As described above, by annealing carried out in atmospherecontaining oxygen after film formation, P₂O₃ is converted into P₂O₅ tostabilize the PSG film 15 b. Moreover, the final composition of P₂O₅provides a passivation effect to the PSG film 15 b, and contributes tothe stabilization of an interface characteristic. Noted that residualcarbon in the formed film is simultaneously oxidized by the annealing.

[0108] Then, an oxygen flow rate is adjusted to 6 SLM while thesubstrate temperature is maintained at 650° C., hydrogen is newly addedat a flow rate of 5 SLM, and then these are introduced through a burningheater into the chamber. The burning heater is heated to 850° C.beforehand. Mixed gas is ignited to cause reaction so as to generatewater molecules, and as shown in FIG. 9E, heating is carried out inatmosphere containing moisture for about 15 minutes. Since an oxidizingforce for the heating carried out in the moisture containing atmosphere,so-called steam annealing is stronger than that for normal oxygenannealing, film quality can be further improved by oxidizing residualIII valance phosphorus, and increasing the moisture absorptionresistance. By examination, the reduction in the amount of moisture inthe film to about {fraction (1/10)} was verified. A reason for such areduction is not yet definite. However, a likely reason may be that amoisture absorbing site remaining in the network of SiO₂ can be greatlyreduced by strong oxidation provided by the steam annealing.

[0109] As apparent from the foregoing, according to the secondembodiment of the present invention, since insulating films 21 and 15having high-concentration of P₂O₃ as a phosphorous component are formed,a fluidization temperature can be reduced to 700° C. or much lower.Accordingly, such a film can be used as an interlayer insulating film tocover aluminum wiring. Moreover, even when such a film is used as thebase insulating film of a wiring layer in a semiconductor device havinga narrower diffused layer with a higher densification of thesemiconductor device, impurities in the diffused layer can be preventedfrom being re-distributed.

[0110] Further, the necessity of a flattening processing technology suchas a CMP method or the like can be eliminated, and the interlayerinsulating film can be flattened by thermally fluidizing the formedfilm. Thus, a recessed part between the wiring layers can be filledwithout any gaps.

[0111] Assuming that nitrogen is used as carrier gas, since N₂ is adiatomic molecule, when a film is formed by reaction of the plasmaenhanced deposition gas, N₂ is prone to be dissociated, leaving ammonia(NH3) in the formed film. According to the second embodiment of thepresent invention, inert gas, e.g., argon or helium, is used as carriergas. Because of little reactivity of argon or helium itself, suchinterference compound can be prevented from forming.

[0112] Further, by using inert gas as carrier gas, a concentration ofphosphorus was greatly reduced during heat treatment after filmformation, enhancing controllability of the concentration of phosphorus.

[0113] In addition, by forming a film using only a phosphorus containingcompound, which contains III valance phosphorus, the amount of carbonleft in the formed film can be greatly reduced. In this case, theadjustment of concentration of phosphorus can be made by controlling theratio of flow rates between the silicon and phosphorus-containingcompound and the inert gas in the deposition gas. Thus, the addition ofa compound containing silicon but no phosphorus, which is conventionallyadded to the deposition gas was made unnecessary in principle. Also, thecompound containing silicon but no phosphorus has Si—C bonding, causingcarbon to be left in the formed film. Thus, such a compound shouldpreferably be added as little as possible. However, addition thereof maybe permitted as occasion demands.

[0114] In addition, after film formation, so-called steam annealing iscarried out, which heats the formed film in atmosphere containingmoisture after nitrogen annealing and oxygen annealing. Since the steamannealing has a stronger oxidizing force than that of normal oxygenannealing, film quality can be further improved.

[0115] The invention has been described in detail with reference to thepreferred embodiments. However, the scope of the invention is notlimited to the specified embodiments. Various changes and modificationscan be made without departing from the gists of the invention, and suchchanges and modifications are within the scope of the invention.

[0116] For example, in the second embodiment, no oxygen is used fordeposition gas. Needless to say, however, as in the case of the firstembodiment, by adding oxygen, a melting temperature or a fluidizationtemperature can be adjusted by controlling a concentration of P₂O₃ orthe ratio of P₂O₃/P₂O₅. In addition, by controlling other depositionparameters, e.g., a substrate temperature and the flow rate of inertgas, as in the case of the first embodiment, a melting temperature or afluidization temperature can also be adjusted through the adjustment ofa concentration of P₂O₃ or the ratio of P₂O₃/P₂O₅.

[0117] Further, the PE-CVD method is used. However, a TH-CVD method foractivating deposition gas by heat may be used. In this case, forexample, deposition conditions described in Table 7 can be used. TABLE 7TH-CVD Method Deposition parameter Deposition condition Substratetemperature 200 to 400° C. Ozone concentration  0.3 to 2.5% Gas flowrate of SOP-11(b)  0.1 to 1.5 slm Gas flow rate of TMB or TEB  0.1 to1.0 slm

[0118] Also, in the case of the TH-CVD method, ammonia may be generatedwhen N₂ is contained in deposition gas. However, by using a compoundcontaining no N₂ in the deposition gas, the amount of ammonia in theformed film can be reduced substantially to zero.

[0119] In stead of the foregoing annealing, or together with annealing,a cover insulating film for moisture absorption prevention may be formedon the PSG film 15 b.

[0120] As a CVD apparatus, the TH-CVD apparatus or the PE-CVD apparatusis used, and the furnace for annealing is used to improve the filmquality. However, in order to enable the film to be reformed withoutexposure to atmosphere after film formation, a film forming apparatusentirely having a constitution, where the CVD apparatus and theannealing furnace are connected by a load-lock chamber should preferablybe used.

[0121] As apparent from the foregoing detailed description, the presentinvention is advantageous in the following respects. Since the PSG filmor the BPSG film is formed in a state of oxygen shortage, the PSG filmor the BPSG film having a high-concentration of P₂O₃ as a phosphorouscomponent can be formed, making it possible to reduce a fluidizationtemperature to 700° C. or much lower. Thus, such a film can be used as aflattened base film below the wiring layer, or a flattened interlayerinsulating film to cover the wiring layer.

[0122] Since the interlayer insulating film can be flattened bythermally fluidizing the formed film, a recessed part between the wiringlayers can be filled without any gaps.

[0123] Inert gas, e.g., argon or helium, is used as carrier gas,.Because of little reactivity of argon or helium itself, the amount ofammonia in the formed film can be reduced substantially to zero, makingit possible to improve film quality.

[0124] Furthermore, by using inert gas as carrier gas, a concentrationof phosphorus is greatly reduced during heat treatment after filmformation, making it possible to enhance controllability of theconcentration of phosphorus.

What is claimed is:
 1. A film-forming method, comprising the steps of:preparing deposition gas containing an inert gas, and a silicon andphosphorus-containing compound having III valance phosphorus in whichoxygen is bonded to at least one of bonding hands of phosphorous; andforming a silicon containing insulating film containing P₂O₃ on asubstrate by using said deposition gas.
 2. The film-forming methodaccording to claim 1 , wherein said silicon and phosphorus-containingcompound, having III valence phosphorus in which oxygen is bonded to atleast one of bonding hands of phosphorous, is one selected from thegroup consisting of silicon and phosphorus-containing compounds havingstructural formulas described below.


3. The film-forming method according to claim 1 , wherein said inert gasis the one selected from the group consisting of argon (Ar) and helium(He).
 4. The film-forming method according to claim 1 , wherein saiddeposition gas contains a silicon compound containing no phosphorus. 5.The film-forming method according to claim 1 , wherein said depositiongas contains oxygen atoms.
 6. The film-forming method according to claim1 , wherein said deposition gas is excited by heating, alternatively byconversion into plasma.
 7. The film-forming method according to claim 1, wherein said substrate during the film formation is heated to atemperature set in a range of 20 to 400° C., alternatively thetemperature is adjusted.
 8. The film-forming method according to claim 1, wherein said silicon containing insulating film containing P₂O₃ is theone selected from the group consisting of a phospho-silicate glass film(PSG film) and a boro-phospho silicate glass film (BPSG film).
 9. Thefilm-forming method according to claim 1 , wherein after the step offorming said silicon containing insulating film containing P₂O₃, saidformed film is further heated, fluidized and flattened.
 10. Thefilm-forming method according to claim 9 , wherein a temperature forheating said formed film is set equal to 700° C., alternatively lower.11. The film-forming method according to claim 9 , wherein after saidformed film is heated, fluidized and flattened, said formed film isfurther heated in atmosphere containing oxygen, and P₂O₃ in said formedfilm is converted into P₂O₅.
 12. The film-forming method according toclaim 11 , wherein after said formed film is heated, and P₂O₃ in saidformed film is converted into P₂O₅, said formed film is further heatedin atmosphere containing moisture.
 13. The film-forming method accordingto claim 1 , wherein after said silicon containing insulating filmcontaining P₂O₃ is formed, said formed film is further heated inatmosphere containing oxygen, and P₂O₃ in said formed film is convertedinto P₂O₅.
 14. The film-forming method according to claim 13 , whereinafter said formed film is heated, and P₂O₃ in said formed film isconverted into P₂O₅, said formed film is further heated in atmospherecontaining moisture.
 15. A manufacturing method of a semiconductordevice, comprising the steps of: forming a wiring layer on an insulatingfilm; preparing deposition gas containing an inert gas, and a siliconand phosphorus-containing compound having III valance phosphorus inwhich oxygen is bonded to at least one of bonding hands of phosphorous;and forming a flattened silicon containing insulating film containingP₂O₃ and covering said wiring layer by using said deposition gas. 16.The manufacturing method of a semiconductor device according to claim 15, wherein a material for said wiring layer is the one selected from thegroup consisting of aluminum, an aluminum alloy, copper, and a copperalloy.